Apparatus for moulding helical gears by compression of powders

ABSTRACT

Helical gears are formed by powder compression by means of a die having a toothed internal profile corresponding to that of the gear to be molded, a movable punch having an externally toothed portion adapted to enter the die to compress the powder, and an internally toothed guide means to guide the portion with a helical motion into the die to cause the external toothing of the portion to mate correctly with the internal toothing of the die.

I United States Patent 1 1 [111 3,891,367 Signora 1 June 24, 1975 [54]APPARATUS FOR MOULDING HELICAL 2,767,428 10/1956 Pingel 425/79 GEARS BYCOMPRESSION 0F POWDERS g; 55 425/78 1 1 [75] Inventor: Maurizio Signora,Palazzo Canavese Italy Primary Examiner-Robert L. Spicer, Jr. [73]Assignee: lng. C. Olivetti & C., S.p.A., Attorney, Agent, or Firm-Ira.I. Schaefer Ivrea (Torino), Italy [22] Filed: May 8, 1973 [57] ABSTRACT[21] .lppl. No.2 358,426 Helical gears are formed by powder compressionby means of a die having a toothed internal profile corre- 52 U.S. Cl.425/78; 425/354; 425/443 spmdmg 9 that of the gear be F a Mable punchhavmg an externally toothed portion adapted to [51] Int. Cl. B22f 3/02,B22f 5/08 enter the die to compress the powder and an inter 4 [58] Fleldof Search 425/78 354 43 nally toothed guide means to guide the portionwith a [56] References Cited helical motion into the die to cause theexternal toothmg of the portion to mate correctly with the internalUNITED STATES PATENTS toothing of the 2,379,540 7/1945 Morris 425/782,561,735 7/1951 Haller 425/78 5 Claims, 4 Drawing Figures APPARATUS FORMOULDING HELICAL GEARS BY COMPRESSION OF POWDERS BACKGROUND OF THEINVENTION 1. Field of the Invention The present invention relates to anapparatus for moulding helical gears by compression of powders, whereinan externally toothed movable punch is guided with a helical motion intoan internally toothed die.

2. Description of the Prior Art Apparatus of the aforesaid type isknown. A first known apparatus comprises a non-rotatable die, theinternal profile of which corresponds to the external profile of thegears to be moulded, and two opposed punches each having one endprovided with helical toothing adapted to engage with the die. Thesepunches are rotated during the compression operation, each by means ofan internally and externally toothed sleeve, the inner part of whichengages a helical toothing of the punch separate from that at the end ofthe punch itself, while the outer part engages another helical toothingwhich is non-rotatable. This apparatus does not allow equality to beobtained with sufficient precision between the pitch of the helicalmovement imparted by the sleeve to the punch and the pitch of thetoothing of the die. In fact, in order to avoid the compacted gearhaving considerable flashes, the clearance between each punch and thedie must not be greater than a few hundredths of a millimetre and,therefore, the set of toothings by which the two punches are rotatedshould be produced with tolerances of the order of ten thousandths of amillimetre. This cannot be achieved practically speaking and, therefore,to ensure the absence of a abnormal contacts between the punches and thedie it is necessary to leave a clearance greater than that desired, withthe result of obtaining compacted bodies with considerable flashes andwhich are therefore inferior. Moreover, in view of the precision withwhich this set of toothings must be constructed, this known apparatus isvery costly. Finally, with this apparatus it is necessary to add a thirdpunch to be able to produce a helical gear with a hub, and on the latterit is not possible to form projections, such as, for example, keysintegral with the hub itself.

A second known apparatus comprises a fixed helical die which is engagedby the ends of two helical punches movable in opposite directions. Thepunches are rotated through the agency of two racks and paired worms andworm wheels. The lower punch is arrested within the die to form thechamber into which the powder is loaded. Thereafter, the upper punchenters the die and compresses the power against the lower die, whichremains stationery during the compression process. This apparatus isalso very complicated and does not permit perfect equality between thepitch of the movement of the punches and the pitch of the toothing ofthe die. This is because of the practically speaking unrealizableprecision with which the elements of the mechanisms by which the punchesare rotated would have to be constructed so that between the punches andthe die there may be a clearance which does not give rise to theformation of considerable flashes on the compacted body. Moreover, thecompacting of the powder is not uniform inasmuch as the compressionstroke is performed by the upper punch only.

If it is desired to form helical gears with a hub, a rotation of thepowder within the empty spaces of the helical die is effected during thecompression, while the friction between the punches and the remainingpowder tends to keep the latter stationary. If frequenlty happens,therefore, that the gear which is formed breaks, espacially in thedividing plane between the hub and the gear. This shortcoming isinsurmountable in the case where the gear to be obtained has its hubprovided with projections, such as, for instance, seats for keys or keysintegral with the hub.

OBJECTS AND SUMMARY OF THE INVENTION According to the present invention,there is provided apparatus for moulding helical gears by compression ofa powder, comprising a die having a toothed internal profilecorresponding to that of the gear to be moulded, a movable punch havingan externally toothed portion adapted to enter the die to compress thepowder, and an internally toothed guide means within which the saidportion moves so as to guide the said portion with helical motion intothe die and cause the external toothing of the portion to mate correctlywith the internal toothing of the die.

BRIEF DESCRIPTION OF THE DRAWINGS The following description presents, byway of example, a preferred embodiment and is given with reference tothe accompanying drawings, in which:

FIG. 1 is a perspective view of a gear to be moulded by the apparatusembodying the invention;

FIG. 2 is a median section of the moulding apparatus in the initialstage of its operation,

FIGS. 3 and 4 show the apparatus of FIG. 2 in two following stages ofits operation.

DETAILED DESCRIPTION OF THE INVENTION The gear 10 (FIG. 1) is to beproduced by the powder compression and sintering process. The gear 10has a part 11 with helical teeth and a hub 12 comprising a key 13. Thegear 10 is moreover provided with a through bore 14.

The moulding apparatus includes an upper die 16 (FIG. 2) which is fixedand a lower die 17 movable in the axial direction. The upper die 16 hasa profile corresponding to the external profile of the toothed gear part11 and is provided with two locating pins 18. The pins 18 have theirlower ends fast with the upper die 16, are provided with a taperedcentering portion 27 at the upper end and project in a perpendiculardirection from the upper surface of the die 16. From the upper die 16there moreover project, four like bearing feet 26 (only two of which areshown in FIG. 2).

The lower die 17 has an internal profile corresponding to the externalprofile of the hub 12 and the key 13.

A lower punch 19 which is hollow internally and has its external profilecorresponding to that of the external surface of the hub 12 and the key13 can cooperate with the lower die 17. The lower punch 19 is movablevertically. Moreover, a core 20 is housed in the hollow space of thelower punch 19 and is vertically movable with respect thereto forforming the hole 14.

The lower end 21 of an upper punch 22 which is hollow internally toallow the passage of the core 20 can cooperate with the upper die 16.The external profile of this end 21 corresponds to the external profileof the toothed gear part 11. The upper punch 22 is rotatable in asupport comprising an assembly of rolling bearings indicated generallyby the reference 23 and is movable vertically together with the support23.

A guide plate 24 is movable vertically and is provided with an opening30 in which is inserted a block 31 having a toothed internal profile,that is to say a nut, exactly like the profile of the upper die 16. Theend 21 of the upper punch 22 is always in mesh with the block 31. Theplate 24 is provided with two locating holes 25 adapted to engage overthe pins 18 of the upper die 16.

The apparatus operates in the following manner. In the first stage, thecharging stage, the lower die 17 is in the highest position with its ownupper surface in contact with the lower surface of the upper die 16. Thelower punch 19 is inside the lower die 17, the core 20 is in the highestposition, substantially level with the upper surface of the upper die16. The plate 24 is located in the highest position and the upper punch22 is located in the most elevated position with respect to the plate 24itself, that is to say substantially in line with the bottom surface ofthe block 31. This is the situation illustrated in FIG. 2.

The metal powder is charged into the dies 16 and 17 in manner known perse. After the charging operation, the upper punch 22 (FIG. 3) and theplate 24 descend together vertically until the plate 24 is arrestedagainst the upper die 16 by bearing against the feet 26. In the lastpart of this movement the two pins 18 centre the holes 25 by means ofthe tapered portions 27 and then insert themselves therein and positionthe plate 24 angularly, so that when the latter is arrested against thefeet 26 of the upper die 16, the toothed profile of the block 31 andthat of the upper die 16 are exactly in phase with one another. Thelocating pins 18 therefore correct any possible angular displacements ofthe plate 24 which may occur during the preceding movements. The feet 26are necessary in order to avoid any powder which may possibly havefallen on to the upper die 16 during the charging operation altering thestop position of the plate 24, with consequent angular displacement ofthe profile of the block 31 with respect to that of the die 16. To thisend, the feet 26 are made higher than the charging level of the powder,which coincides substantially with the upper surface of the upper die16.

When the plate 24 is arrested, the upper punch 22 continues to descendwith a helical motion, guided by the block 31 of the same plate 24. Theend 21 of the punch now engages with the upper die 16 to compress thepowder in the die 16, while the lower punch 19 moves simultaneously inthe opposite direction without rotating to compress the powder in thedie 17, reaching the position shown in FIG. 3.

It is necessary to note that the internal profiles of the block 31 ofthe plate 24 and of the upper die 16 can be obtained exactly alike,since these last-mentioned parts are substantially two plates which aresuperimposable and, therefore, machinable at the same time with the sametool. The end 21 of the upper punch 22 therefore moves within the upperdie 16 with a motion exactly equal or corresponding to the helix of thedie 16. Moreover, rotary movements do not occur between the powdercompressed in the upper die and the powder which forms the hub of thegear, so that the part formed does not present weak zones.

The extraction of the compacted part now begins. First of all, the coreis lowered. When it has cleared the hole 14, the lower die 17 descendsbelow the hub 12 of the gear 10, which in the meantime is held up by thelower punch 19, which has remained in the highest position adopted atthe end of compression, as in FIG. 3. The lower punch 19 is then loweredand then, together with the lower die 17 and the core 20, is brought tothe lowest position of extraction, as in FIG. 4. The upper punch 22 isthen lowered further and pushes the gear 10 out of the upper die 16.Suitable means (not shown in the drawings) are pre-arranged to beintroduced below the gear 10 for the purpose of receiving it andremoving it from the moulding apparatus.

The apparatus is then returned to the initial charging position shown inFIG. 2. The apparatus is now ready to receive a new charge of powder.

It is obvious that the gear 10 is only illustrative, it being possibleto produce gears of different form, for example helical gears with thehub provided with openings having axial symmetry in addition to beingprovided with keys, or with special shapings of the base surface of thehub, etcetera.

I claim:

1. Apparatus for moulding helical gears by compression of a powder,comprising a die member having a toothed internal profile correspondingto that of the gear to be moulded, a movable punch having an extcrnallytoothed portion adapted to enter the die member to compress the powder,a guide member adapted to cause said portion to move with a helicalmotion with the same pitch as the said profile, said guide membercomprising a female threaded member directly in engagement with theportion of the punch, and being movable towards the die member, andmeans for angularly positioning the guide member in an angular positionfixed with respect to said die member, wherein said means for effectingangular positioning comprises at least one pin adapted to be introducedinto a corresponding hole during movement of said guide member towardssaid die member, one of said members being provided with said pin andthe other of said members being provided with said hole, stop means forthe guide means being carried by one of said members and being such thatwhen the guide is arrested by the stop means, the means for effectingangular positioning align the toothing of the punch portion with thetoothing of the die.

2. Apparatus as in claim 1, wherein said stop means comprises at leastthree bearing feet disposed in the same plane parallel to the surface ofthe die and being adapted to arrest said guide means with a clearancebetween said guide means and said die.

3. Apparatus as in claim 1, wherein said pin is carried by said diemember and said hole is provided in said guide member.

4. Apparatus for moulding helical gears by compression of a powder,comprising a die member having a toothed internal profile correspondingto that of the gear to be moulded, a movable punch spaced from the diemember and having an externally toothed portion adapted to enter the diemember to compress the powder, and guide means for angularly positioningsaid externally toothed portion with respect to said toothed internalprofile for allowing the portion to enter the die member, said guidemeans comprising a female threaded member separate from the die memberand directly in engagement with said externally toothed portion of thepunch.

5. Apparatus as in claim 4, wherein said female threaded member ismovable towards the die member and wherein said guide means furthercomprises means for angularly positioning said female threaded member inan angular position fixed with respect to said die member.

1. Apparatus for moulding helical gears by compression of a powder,comprising a die member having a toothed internal profile correspondingto that of the gear to be moulded, a movable punch having an externallytoothed portion adapted to enter the die member to compress the powder,a guide member adapted to cause said portion to move with a helicalmotion with the same pitch as the said profile, said guide membercomprising a female threaded member directly in engagement with theportion of the punch, and being movable towards the die member, andmeans for angularly positioning the guide member in an angular positionfixed with respect to said die member, wherein said means for effectingangular positioning comprises at least one pin adapted to be introducedinto a corresponding hole during movement of said guide member towardssaid die member, one of said members being provided with said pin andthe other of said members being provided with said hole, stop means forthe guide means being carried by one of said members and being such thatwhen the guide is arrested by the stop means, the means for effectingangular positioning align the toothing of the punch portion with thetoothing of the die.
 2. Apparatus as in claim 1, wherein said stop meanscomprises at least three bearing feet disposed in the same planeparallel to the surface of the die and being adapted to arrest saidguide means with a clearance between said guide means and said die. 3.Apparatus as in claim 1, wherein said pin is carried by said die memberand said hole is provided in said guide member.
 4. Apparatus formoulding helical gears by compression of a powder, comprising a diemember having a toothed internal profile corresponding to that of thegear to be moulded, a movable punch spaced from the die member andhaving an externally toothed portion adapted to enter the die member tocompress the powder, and guide means for angularly positioning saidexternally toothed portion with respect to said toothed internal profilefor allowing the portion to enter the die member, said guide meanscomprising a female threaded member separate from the die member anddirectly in engagement with said externally toothed portion of thepunch.
 5. Apparatus as in claim 4, wherein said female threaded memberis movable towards the die member and wherein said guide means furthercomprises means for angularly positioning said female threaded member inan angular position fixed with respect to said die member.